In the art of vegetation cutting implements, and methods of cutting vegetation utilizing such implements, it is highly desirable to be able to easily replace or replenish the cutting elements, to provide durability and long life thereof, to provide simplicity of mechanisms and operation, and to provide effective cutting of the vegetation with a minimum of fuel consumption (that is high aerodynamic efficiency). These desirable criteria are provided according to the present invention by utilizing a plurality of self-supporting struts instead of utilizing standard strings or filaments as the actual cutting elements (such as shown in U.S. Pat. Nos. 4,571,831 and 5,048,278, for example).
The self-supporting struts according to the present invention have the same basic desirable quantities of string or filament cutting elements, that is while effectively cutting vegetation doing minimal harm to solid objects that they might encounter, and thereby enhancing safety. The struts are made of more than 50% non-metallic material, typically more than 90% plastic or rubber, as described in said co-pending application Ser. No. 09/010,992. By "self-supporting" is meant when the end of the strut closest to the central axis of the vegetation cutting implement is supported, the free end of the strut has a deflection, based upon its own weight, of only a few degrees or less, e.g. about 5.degree. or less. The self-supporting struts according to the invention are easy to provide in a configuration and mechanism that allows the orientation of the strut to be maintained with an appropriate orientation which is particularly important when the strut has an aerodynamic configuration (such as described in the parent applications), but which can be helpful even if the strut has a conventional cross-section (e.g. circular).
According to one aspect of the present invention, a method of cutting vegetation using at least one cutter head having a plurality of self-supporting struts each comprising more than 50% non-metallic material and each having a beam-like structure with a first axis which is the strongest axis and has the highest moment of inertia, and a second, weaker, axis. The method comprises the steps of: (a) Rotating the head with self-supporting struts about an axis of rotation so that the first axis of the beam-like structure of each strut is positively maintained and moves in a predefined cutting plane. And, (b) bringing the rotating self-supporting struts into contact with vegetation so that the cutting plane is generally transverse to a portion of the vegetation to be cut, and the self-supporting struts cut the vegetation.
Typically step (a) is practiced at a speed of at least 2000 rpm, typically on the order of 5000-12000 rpm depending upon the diameter of the cutting swath, e.g. 15,000-20,000 fpm for the trip of the element, and there is also typically the further step (c) of replacing a plurality of self-supporting struts when worn, either individually, or--where the self-supporting struts are substantially integral with a central hub--by replacing the central hub. Compared to the speed of rotation of conventional string trimmers (27,000-30,000 fpm), trimming according to the invention is much more efficient so that a speed as low as 15,000-20,000 fpm for the trip is effective.
The central hub may comprise a substantially annular element, and the cutter head may comprise first and second elements which clamp together. Step (c) is then practiced by unclamping the first and second head elements, replacing the central hub and properly positioning the self-supporting struts, and clamping the replaced central hub and substantially integral self-supporting struts between the first and second head elements. The central hub may comprise the rotatable head, which attaches to a rotatable shaft, in which case step (c) is practiced by detaching the head from the shaft and reattaching the head to the shaft. The head may comprise the end of the shaft, and radial clearance space may be provided between the shaft and the central hub, in which case step (c) is practiced by inserting a plurality of retaining elements and the radial clearance between the head and central hub. The head may comprise an open bottom annular element with a plurality of substantially radially extending bores with the struts, though self-supporting, being bendable; in this case step (c) is practiced by bending and threading the struts through the bores and pulling and pushing the struts into the open bottom annular element.
The head may comprise a disc-shaped element having a plane substantially perpendicular to the axis of rotation of the head, at least one support extending from the element substantially parallel to the axis of rotation and having a plurality of strut-receiving openings therein; and wherein step (c) is practiced by pulling radially on each existing strut to be replaced to remove it from its opening, and radially inserting a new strut into the opening.
According to another aspect of the present invention a vegetation cutting implement is provided comprising the following components: A rotatable cutter support had at the end of a supporting shaft. A power source capable of rotating the rotatable head and operatively connected thereto. And, a plurality of cutter elements releasably mounted to the rotatable cutter support head; and each cutter element comprising a self-supporting strut comprising more than 50% non-metallic material. Preferably each of the struts has a beam-like structure with a first axis which is the strongest axis and has the highest moment of inertia, and a second, weaker, axis; and wherein the elements are mounted to the cutter support head so that during rotation of self-supporting struts about an axis of rotation the first axis of the beam-like structure of each strut is positively maintained and moves in a predefined cutting plane.
The head may have a generally truncated cone configuration depression, and the plurality of cutter elements may be part of a cartridge hub; in which case the cartridge hub has a surface with a generally truncated cone configuration, matching that of the depression, the surface being received within the depression. The implement may further comprise a first fastener extending generally centrally outwardly from the depression, through a substantially central opening in the hub, and a second fastener cooperating with the first fastener to hold the hub in the depression (e.g. the first fastener comprising a screw threaded fastener such as a bolt, and the second fastener comprising a nut or the like). Typically the cutter elements are integral with a central hub, although they may be mounted by a central hub having a plurality of generally radial openings through which the cutter elements pass, in which case the cutter elements are individually replaceable in the openings. Webbing may extend between the cutter elements to facilitate positioning them and to ensure the generally self-supporting nature thereof. Typically three to eight cutter elements are provided.
The invention also relates to a replaceable hub with cutter elements for a vegetation cutter. The hub comprises: A generally annular central body portion having a central bore. A plurality of self-supporting strut cutter elements extend radially outwardly from the body portion and substantially evenly spaced circumferentially around the hub. And, each of the strut cutter elements comprising more than 50% rubber or plastic, so that a cutter element will flex when it impacts a stationary solid object such as a tree or fence. The elements may be integral with the hub body portion or the hub body portion may have a plurality of radially extending openings and a distinct cutter element passing into each opening.
It is the primary object of the present invention to provide a simple yet effective and advantageous method of cutting vegetation using a rotating cutter head, and a vegetation cutting implement and replaceable hub for use therein. This and other objects of the invention will become clear from an inspection of the detailed description of the invention and from the appended claims.